The present invention relates to a class-D amplifier suitable for a power amplifier in audio equipment or the like.
A class-D amplifier is an amplifier for generating a pulse train having a pulse width modulated in correspondence to an input signal, so that the pulse train drives a load. In many cases, such a class-D amplifier is employed as a power amplifier for driving a speaker in audio equipment or the like. A class-D amplifier of this kind is disclosed in JP-A-2007-124624.
Meanwhile, in audio equipment equipped with a class-D amplifier, a mute function is necessary in some cases. In the prior art, in order that such a requirement should be satisfied, an attenuation circuit or a volume circuit implemented by an operational amplifier has been provided in the input section of the class-D amplifier so that a mute function has been realized. Nevertheless, such an attenuation circuit or a volume circuit causes an increase in the circuit size and in the cost of the class-D amplifier. Further, another problem has been caused that the attenuation circuit or the volume circuit need be controlled in the class-D amplifier and hence the control becomes complicated.